Template-free synthesis of hierarchical TiO2 hollow microspheres as scattering layer for dye-sensitized solar cells

•Hierarchical TiO2 hollow microspheres were synthesized via a template-free route.•The formation mechanism of inside-out Ostwald ripening was verified by using SEM/TEM.•An efficiency of 7.84% was achieved by using the hollow spheres as scattering layer.•Improved efficiency was attributed to the enhanced dye-loading and light scattering. Hierarchical TiO2 hollow microspheres were synthesized by a 2-step process consisting of thermal hydrolysis and subsequent solvothermal reaction. Quasi-monodispersed solid TiO2 microspheres aggregated by amorphous particles were firstly obtained by the controlled thermal hydrolysis of titanium sulfate, and then the solid structures transformed to hollow ones and crystallized during the subsequent solvothermal treatment. SEM and TEM images of the samples revealed that the morphological evolution was in perfect accordance with the inside-out Ostwald ripening mechanism. The rich porosity and unique hierarchical hollow structure endow the TiO2 microspheres with a large specific surface area of 108.0m2g−1. As an effective anode material for dye-sensitized solar cells, TiO2 hollow microspheres showed good capability of dye adsorption and strong light scattering, leading to a comparable energy conversion efficiency to the commercial 18NR-T transparent titania. Finally, a high efficiency of 7.84% was achieved for the bi-layer DSSC by coating the hollow microspheres on top of the 18NR-T titania as the light scattering layer.